A free 3D game engine to create games and realtimes scenes for Windows
Spring is a free RTS engine developed for Windows, Linux and Mac OS X.
A cross platform Lua based game engine
Planimeter Game Engine 2D - LÖVE-based game engine for Lua
Game engine for playing tomb raider 1 - 5 levels.
Pear3DEngine is a modern and modular 3D development framework
Make games with Lego-like building blocks